Kinetics of niobium carbide coating produced on AISI 1040 steel by thermo-reactive deposition technique

There are a lot of technologically interesting characteristics of niobium carbide coating deposited by pack method which is the production of hard, wear-resistant, oxidation and Corrosion resistant coating layer on the steel substrates. In the present study, the growth kinetics of niobium carbide layer deposited by thermo-reactive diffusion techniques in a solid medium on steel samples was reported. Niobium carbide coating treatment was performed on AISI 1040 steels in the powder mixture consisting of ferro-niobium, ammonium chloride and alumina at 1073, 1173 and 1273 K for 1-4 h. The presence of NbC and Nb2C phases formed on the surface of the steel substrates was confirmed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analyses. Niobium carbide layer thickness ranges from 3.42 +/- 0.52 to 11.78 +/- 2.29 mum depending upon the treatment time and temperature. Layer growth kinetics was analyzed by measuring the depth of niobium carbide layer as a function of time and temperature. The kinetics of niobium carbide coating by pack method shows a parabolic relationship between carbide layer thickness and treatment time, and the activation energy for the process is estimated to be 91.257 kJ mol(-1). Moreover, an attempt was made to investigate the possibility of predicting the contour diagram of niobium carbide layer variation and to establish some empirical relationships between process parameters and niobium carbide layer thickness. (C) 2004 Elsevier B.V. All rights reserved.